Drill bits containing fixed cutters (such as PDC cutting elements) are generally designed by distributing the fixed cutters along a cutter profile (viewed from the side of the drill bit) that extends radially from the axis of the drill bit to the gauge (outer diameter) of the drill bit. The fixed cutters may be placed at varying positions along the cutter profile.
In the prior art, the shape of the cutter profile is typically some combination of a depression at the drill bit axis transitioning from a straight line into an arc, parabola or series of arcs that extend radially to the gauge of the drill bit. The depression is typically referred to as the cone portion of the drill bit and the arcs are usually referred to as the nose portion and shoulder portion of the drill bit. An example of this type of cutter profile can be seen in U.S. Patent Application Publication No. US 2011/0127089 (Beaton).
It is generally believed that the stability of a drill bit is enhanced by the cone portion of the drill bit. One theory is that during drilling, a conical region of rock is left by the cone portion of the drill hit which tends to reduce lateral movement of the drill bit, maintain concentric rotation of the drill bit, and mitigate damaging vibrations. It is also generally believed that the deeper the cone portion (and the steeper the cone portion), the more stability that is generated.